Reporting from Sacramento -- Gov. Jerry Brown, whose signature more than three decades ago gave agricultural workers the right to unionize by secret ballot, vetoed a bill Tuesday that would have made it easier for farm laborers to organize.

The proposal has been the top legislative goal for years for the United Farm Workers, whose founder, Cesar Chavez, had strong ties to Brown. It would have allowed the union to bargain for employees without holding an election — by simply collecting signatures from a majority of workers on cards saying they wanted representation.

Gov. Arnold Schwarzenegger vetoed similar measures four times during his seven years in office. Supporters of the latest bill had been hopeful that Brown, a Democrat who often spoke of his relationship with Chavez during his gubernatorial campaign last year, would approve it.

In his veto message Tuesday, Brown cited his work with the union 36 years ago.

"I am not yet convinced that the far-reaching provisions of this bill … are justified," Brown wrote.

Union leaders reacted angrily.

"To us it's a real clear decision," UFW President Arturo Rodriguez said. "This governor has decided to side with the rich against the powerless."

The veto highlights the diminishing clout of the UFW, which once commanded the attention of national leaders, including Robert F. Kennedy. The group's influence has been eroding steadily. Membership has dwindled from about 26,000 a decade ago to just over 5,200 last year, according to statistics that the union provided to the U.S. Department of Labor.

The pressure on Brown to sign the bill, SB 104, by state Senate leader Darrell Steinberg (D-Sacramento), was intense. For nearly two weeks, UFW representatives flooded the Capitol, urging Brown to approve the measure. They held protests and vigils outside Brown's office and even brought Chavez's chair to the governor, inviting him to sit in it and ratify the legislation.

Steinberg's bill was a priority for Democrats this year and one Republicans fiercely opposed. The governor's veto — on the heels of a budget deal struck with Democrats alone — helps keep him in the political center. Brown has often referred to such centrism as "the canoe theory" of governing: paddling a little on the left, a little on the right and staying in the middle.

The union enlisted many of the state's top Democratic leaders to solicit the governor's signature. They included Los Angeles Mayor Antonio Villaraigosa and Rep. Howard L. Berman (D-Valley Village), who as a state assemblyman wrote the Agricultural Labor Relations Act of 1975.

Opponents of the bill included a large coalition of business and agricultural interests, including the California Chamber of Commerce, the California Grocers Assn., the California Restaurant Assn. and the Western Growers Assn.

They argued that the bill would have created excessive new fines against growers found to be committing unfair labor practices, and the "card check" provision would allow for mischief by union organizers.

"It sets the stage for intimidation by the union," said Tom Nassif, president and chief executive officer of Western Growers. "It doesn't allow a true free choice."

Supporters of the bill countered that growers now coerce laborers into voting against their own interests.

Union leaders vowed Tuesday night that they would try again to win the governor's support.